Review: Space Tethers and Space Elevators

by Jeff FoustMonday, August 3, 2009

August, it would seem, is space elevator month. This weekend the Japan Space Elevator Association is hosting its first technical competition, where battery-powered climbers will attempt to ascend a 150-meter cable held aloft by a balloon. Later this month the 2009 Space Elevator Conference will take place at Microsoft’s headquarters outside Seattle. And until last week, the Space Elevator Games, featuring the beamed power competition with prize money provided by NASA’s Centennial Challenges program, was slated to take place this week at the Dryden Flight Research Center in California (the event was postponed because of technical issues).

Despite this confluence of events, it seems we’re, at best, only incrementally closer to actually being able to build a space elevator than we were when the resurgence of interest in the concept started early this decade. Likewise, the potential of space tethers—close cousins to the space elevator concept, but much less technically challenging given their far shorter lengths—has yet to be realized, despite a number of experiments to date with mixed results. Both concepts are examined in detail by Michel van Pelt’s book, Space Tethers and Space Elevators.

While the book does a good job explaining the technology involved, one aspect it lacks is a discussion why tethers in particular have to date failed to realize their potential.

Tethers get top billing in van Pelt’s book and take up over two-thirds of the book. After an introduction to basic orbital mechanics, he explains how tethers can be used to alter the orbits of spacecraft; the tests that have been done to date with tethers, from early experiments on the final Gemini missions through two failed large-scale tether experiments on shuttle flights in the 1990s to more recent smaller-scale tests; and potential applications of tethers. Two later chapters of the book delve into space elevators, including the history of the concept, the science and engineering involved, and the various challenges involved in trying to build one.

While Space Tethers and Space Elevators does a good job explaining the technology involved, one aspect the book lacks is a discussion why tethers in particular have to date failed to realize their potential. After all, tethers offer the ability to shift orbits without expending propellant, a powerful capability for the typical mass-constrained satellite. Yet the research into tethers has been limited, and the record of flight experiments features a number of failures, the shuttle Tethered Satellite System being the best known but hardly only case. Is this simply a case where insufficient resources have been focused on the technology (and, if so, why), or are there fundamental issues with tether technology that need to be addressed?

Given the mixed record of deploying tethers in space extending several kilometers, it seems unlikely that we’ll see the development of a space elevator—effectively a tether 100,000 kilometers long anchored at one end on the Earth—any time soon. Still, the attractiveness of the technology, which promises to greatly reduce the cost of space access and do away with rockets, means that we’ll see people continue to study it at some low level, through competitions like the Space Elevator Games and various conferences. And who knows: perhaps this will lead to a breakthrough that makes the space elevator technically and financially feasible.

Jeff Foust (jeff@thespacereview.com) is the editor and publisher of The Space Review. He also operates the Spacetoday.net web site and the Space Politics and Personal Spaceflight weblogs. Views and opinions expressed in this article are those of the author alone, and do not represent the official positions of any organization or company, including the Futron Corporation, the author’s employer.